The present invention relates to a microdistillation apparatus and process for the removal of volatile analyte compounds from samples obtained from waste water and other sources.
United States Environmental Protection Agency (EPA) standardized methods for the determination of several chemical species in environmental samples have been established for several years. Based on the technique of flow injection analysis, these methods provide rapid, accurate and precise determinations.
However, for some analytes, notably cyanide, phenolic compounds, ammonia, hydrogen fluoride, volatile acids, sulfides and sulfites, samples must first be taken through a complicated and time consuming distillation process to remove the analyte from a potentially interfering matrix prior to automated analysis. As a result, the analyst has been required to use a low-throughput, large volume manual distillation apparatus and method involving classical vaporization, condensation and collection with expensive and fragile macro-scale glassware.
FIGS. 8 and 9 are examples of the aforementioned current state of the art with respect to macrodistillation apparatus. With these and other systems distillation usually requires two to three hours for completion. These macrodistillation apparatus also typically require as much as 500 milliliters (mL) of sample and therefore can distill only up to five samples simultaneously on an eight foot laboratory bench. Irregular contact between the sample and the mantle is another problem which results in variable heating. When in use these apparatus generate considerable waste heat which often necessitates the use of a fume hood. In addition, current macrodistillation systems employ a water-cooled condenser so that flood safety mechanisms must also be provided for. Transfer is necessary after distillation since the distillate does not end up in a sampler-ready tube. Furthermore, with the current systems there are many separate pieces to both assemble and clean.
Some continuous-flow analyzers employ a flowing-stream digestion and distillation device in which the sample to be determined is fed continuously first into a flow-through UV-irradiation digestion device, and then into a microdistillation chamber. This achieves at best 20 sample/h throughput, with full baseline resolution. These devices also require 30 to 60 minutes of start-up flow to stabilize.
It is now known in the art to utilize hydrophobic membranes to assist in the separation of distillate from distillant. Such membranes are disclosed, for example, in Ohta, U.S. Pat. No. 3,455,792; Cheng, U.S. Pat. No. 4,476,024; Kimura et al., U.S. Pat. No. 4,620,900; and Rodgers, U.S. Pat. No. 3,878,054. However, these membranes are presently employed in conjunction with relatively cumbersome and/or complex distillation apparatus and methods designed to permit a relatively large volume of product to be distilled.
The prior art is thus replete with distillation devices especially well-suited for generating a large volume of distillate, often continuously, for relatively large-scale industrial syntheses. None of these devices are directed towards distillation on a smaller analytical scale, however.
Thus, there presently exists a need for a microdistillation system and method which is relatively simple and which does not require a large volume of sample for efficacy, and therefore is appropriate for analytical-scale distillations of less than 500 mL.